Activation and reactivation of electron emission tubes



Oct. 11, 1932.

L. L. JONES ET AL ACTIVATION AND REAGTIVATION OF ELECTRON EMISSION TUBES Filed Oct. 29. 1929 LESTER L JONES, JDSEPHAFLANZER and EMIL RESMAN,

INVENTORS ATTQRNEYS Patented Oct. 11, 1932' UNITED STATES PATENT? OFFICE" LESTER L. JONES, OF ORADELL, NEW JERSEY, AND JOSEPH A. FLANZER AND EMIL I REISMAN, OE BROOKLYN, NEW YORK, ASSIGNORS TO TEGHNIDYNE CORPORATION,

OF NEW YORK, N. Y., A CORPORATION OF NEW YORK ACTIVATION AND REAGTIVATION OF ELECTRON EMISSION TUBES lpplication'filed October 29, 1929. Serial No. 403,218.

This invention relates to electron emission tubes, and more particularly to a method of activating or reactivating tubes having oxide coated cathodes so as to improve the electron emission thereof. I

' Even though tubes are mechanically similar and undergo identical manufacturing processes large variations are found in the performance of the resulting tubes. Some newly manufactured tubes do not have sufficient emission to pass test, and some tubes have only a very short life. Even the average normal tube has a relatively limited life, say

1000 operating hours, after which it is useless because of reduced cathode emission.

The primary object of our invention is to provide a simple, speedy, and economical method of reactivating used tubes which are no longer satisfactory, particularly due to reduced emission. This we have found to be possible simply by high internal bombardment.

l Vhen the tube has a grid the latter may be overheated owing to its small radiating area, and accordingly a further object of our invention is to apportion the relative heating of the grid and anode so as to prevent overheating of the grid relative to the heating of the anode. Another object of our invention is to provide the desired heating of the tube elements without excessive accompanying electronemission and/or ionization currents which may prove injurious to the tube cathode. A still further object of our invention is to prevent overheating of the tube elements which might cause vaporization of nickel within the tube, and which, if carried still further, might actually destroy the tube elements.

Still another object of our invention is to transfer gas which may be present in the tube electrodes from them to the tube envelope and getter material. A still further object of our invention resides in the provision of a circuit arrangement for the practice of the method of our invention. v

To the accomplishment of the foregoing and I such other objects as will hereinafter appear,

our invention consists in the method steps and their relation one to the other as herein- Referring to the drawing, a tube to be re-' activated, 2, has its cathode 4 connected with variable resistor 8 may be connected in circuit for varying the cathode temperature, and a volt meter 10 used to indicate the terminal potential applied to the cathode. The tube anode 12 maybe connected through a switch 14 to a source of relatively high positive anode potential 16. The value of this potential is not at all critical and may be varled over wide limits, but should be at least equal to the operating potential normally used with tube. In the caseof heater type tubes the heater may be connected in circuit as shown, but the negative terminal of the source 16 is connected to the cathode emitter itself. With heater type tubes direct current as from a battery may be used to heat the cathode, the transformer being especially preferred for directly heated cathodes because during reactivation the plate current is very high, and without the equalization permitted by the center tap and the use of alternating current the cathode'wouldbe very unequally heated along its length.

In accordance with our invention the cathode 4 is heated to a temperature substantially above normal, equivalent to the temperature a source of cathode heating current 6. A

corresponding to say a 50% increase above normal in cathode terminal potential, and at the same time the anode potential is applied to the tube.

The theory behind this method of reactivating the tube cathode is'not certain, but may possibly be explained as follows. During the high internal bombardment which we apply to the tube gas present in the tube is ionized by the electron stream from the cathode, and the positive ions thereof bombard the cathode. The gas to be ionized may be released from the plate by the high velocity electron bombardment, and thereafter ionized. The positive ions hit the cathode with um durlng use.

but this supply of barium is gradually diminished during the use of the tube, inasmuch as.

the rate of formation of barium during the normal use is probably less than the, rate of exhaustion thereof. Our reactivation process probably again forms. a supply of barium suiiicient to make up for a gradual loss there ofover a long period of time, and probably also increases the rate of formation of bari- If the tube 2 has a grid, indicated at 18, this should be polarized in order to help ob tain the desired cathode "emission. The grid may, for example, be connected directly to the anode and both elements treated as a com- "mon anode; This, however, is open to the fault that the grid will ordinarily be overheated relative to the heating of the anode, owing to the very much smaller radiating surface of the grid. It is therefore desirable to apportion the heating of the grid and plate, this we do by applying a reduced potential to the gridrelative to the potential applied to the plate. This may be done by connecting a battery or other suitable source of potential between the, grid and plate. However, there is an advantage in having the grid initially polarized to a high potential in order to help start the electron emission' from the cathode, and for this reason, as

i --well as for the sake of simplicity of apparatus, we prefer to obtain the desired reduction in grid potential by connectirrga resist-- ance between the grid and plate. In this manner the grid is initially polarized at the anode potential, but after space current begins to flow the grid potential is reduced and the reduction thereof is varied in accordance with the grid current flow, so that the potential'and the. heating of the grid are automatically regulated. If a high resistance is connected between the grid and plate the grid potential is aptto-be reduced too. quickly when space current, begins to flow, so that the cathode emission does not have time to get well under way.

We have found that it is desirable tb use a res stance between the'grid and plate having" a hlgh positive temperature coefiicient of re- ,sistance. Such a resistance will remain relatively low in value until sufiicient time has.

elapsed for to. be heated up, and in this period the cathode emission may develop to the; desired point. We find that a. tungsten ,filament lamp forms a suitable resistance for tubes having say one square centimeter of cathode area and four square centimeters of anode area and an amplification constant of 12 we find that a 120 volt tungsten lamp rating between 10 and 25 watts may be used for the resistor 20.

The reduction in grid potential has an additional advantage because *of the resulting increase in tube impedance. What is desired is a high anode temperature, and the temperature obtainable depends upon the power dissipated, which varies as the product of the current and the potential. It is not desirable to have an excessive space current; for that may injure the cathode, and it istherefore necessary to apply a high anode potential. The

aforesaid reduction in grid potential in- I creases the tube impedance and makes it possible to increase the anode potential while ulation of grid potential apportions the heating the grid relative to the heating of the anode. It is further necessary-to limit the overall heating of the bombarded tube elements, for if overheated, nickel contained therein may be vaporized and deposited upon the tube cathode, thereby spoiling the emissivity thereof. vaporization of nickel may be detected by a dark deposit of nickelon the relatively white. oxide-coated cathode of the tube, and also bya darkening of the tube envelope due to a deposit of nickel on thein- Heat radiated from the side wall thereof. The cathode too may con- I deposited upon the cathode lowers its emission, and it is therefore necessary to prevent heat suflicient to vaporize nickel, as well as still more excessive heatin of the tube ele= ments such as'might' phys cally destroy the c For reg I g thespace current through the tube we fifid it desirable to insert in series with the electrodes being bombarded a re: sistance, here exemplified by a tungsten fila ment lamp 22,-. aving a high positive temperature coetfieie t of resistance' This acts as a ballast lamp and provides automatic regulation of the anode pot'ential and consequently of the space current so as to keep the .filament lamp. If the of a metal such as molybdenum or tungsten the current limitation may be increased to say 300 or 400 milli-amperes per square centimeter of cathode area without vaporization of these metals, and consequent injurious coating of the cathode.

At the beginning of the reactivation of the tube it may prove desirable in the case of tubes whichare very gassy to further limit the space current for a period of say half a minute, though We may mention at this point that a very gassy tube may not be worth saving unlessspecial precautions are taken for the reduction of this gas content. The current limitation is desirable because ionization of the gas in the tube may permit an excessively the tube cathode. With such tubes the space current should be held down to say 100 milliamperes per square centimeter of cathode area, and for this purpose a higher resistance may be connected in the anode circuit. In the present case a 120 volt 275 watt tungsten filament lampv 24 is arranged in parallel with resistance 22 so as to be selectively connected in circuit with the tube anode. By throwing switch 14 onto contact 26 during the first part of the activation process there will be no danger of excessive space current due to ionization. A milli-ammeter 28,maybe con nected in the anode circuit, and if the reading thereof is sufficiently small to indicate that the lower resistance 22 may be used, the

switch 14 may then be thrown to the contact 30, thereby applying anode potential to the commutator.

tube through the ballast resistance 22, for the remainder of the activation process.

Switch 14 may further be used to flicker or momentarily interrupt the anode and grid.

although potentials, if this is done manually, it may be mechanically done by means of a The flickering o'f resulting interruptions preferably should remove the anode and grid potentials for eriods of one or two seconds at intervalsco about fifteen seconds. The object of this is to permit of the equivalent of removal of gas from the tube, by causing the gas to be occluded on the inner surface of the tube envelope. The reactivatipn heats up the tube elements sufficiently to drive off gas therefrom. This gas is ionized, resulting in bombardment of the cathode by positiveions, with beneficial effects as previously explained. However, it is desirable to improve the vacuum in the tube and to avoid having gasina distributed state throughout the tube. Ionized gas is subject large space current injurious to to forces of ionization which make it diflicult. I

to condense the gas, whereas molecular gas is freed of ionization forces. By flickering or momentarily interrupting the said potentials periods are provided during which the gas ions may reform into molecules. .These molecules do not condense readily on the tube electrodes, owin to the heated condition of the electrodes. is in a relatively cool state, and the molecular gas therefore tends to go to the walls of the owever, the tube envelope tube or to the getter thereon, where it is condensed and occluded. By flickering or interrupting the said potentials, therefore, we obtain to a limited extent the equivalent of pump evacuation, and the effective gas content of a tube may be considerably reducedby. this method. Flickering or momentary interruption may be used from the beginning of the activation process, or, in the case of tubes with heavier electrodes, may poned long enough for the tube elements to become heated up, after which the flickering or interruptions may be started. 1

The entire reactivation process may take say one minute, but may be continued longer, particularly in order to obtain more flicker-' ing or intermittent periods for condensing free gas in the tube. However, a tube which is not properly reactivated in'say five minutes is probably too far gone to be capable of being reactivated by ourprocess.

From the foregoing explanation it will be clear that it is undesirable to permit heating of the tube envelopes during reactivation, and in fact, it is preferable to provide good air circulation around the tubes, and better still, to actually cool the tubes during the reactivation process, as by means of a fan 40, or more elaborate and efiicient cooling means.

Our process mayalso be tivation of tubes, in contra istinction to reactivation of tubes, that is, the activation of tubes which have not yet been used, rather than used tubes. We find that our invention as aforedescribed may be applied to rejected tubes which cannot pass factory test because of low. cathode emission. A very large percentage of the rejects may be made operative and brought up to normal by applying our activation process.

appliedto the ac- In fac it may prove economical in some shown in the wiringerably have individual ballast lamps, such as the lamps 20, 22, and 24, for independent- 1 1y regulating the grid potential and the space current of each of the tfibcs according to the he postelectron emission characteristic of each of of tubes which are apparently normal under test but which rapidly deterlorate in use is alsogreatly reduced. When-using'the activation step in this manner the possibility of issuing tubes which shortly thereafter become gassy due to gas occluded in the tube electrodes is obviated because during the activation step the bombardment of the electrodes drives gas therefrom, which if small will be removed by condensation of gas on the tube envelope, but which if large will make the tube initially gassy so that it will be rejected and not issued into service.

It will be apparent that while we have shown and described our invention in the preferred form, many changes and modifications maybe made in the method disclosed without departing from the spirit of the invention, defined in the following claims.

We claim:

1. The method of activating electron emission tubes which includes increasing the cathode temperature substantially above normal, applying a high positive anode potential, and holding the space'current within a desired limit depending upon the radiating surface of the anode in order to prevent overheating thereof.

2. The method of activating electron emission tubes which includes increasing the cathode temperatpre substantially above normal and applying a high positive anode potential, and momentarily interrupting the space current by occasionally momentarily interrupting the anode potential.

3. The method of activating electron emission tubes which includes increasing the (33th.

ode temperature substantially above normal and applying a high positive anode poten tial, momentarily interrupting the space cur-- rent by occasionally momentarily interrupting the anode potential, and simultaneously cooling the envelope of the tube.

4. The method of activating electron emis- -sion tubes which includes increasing the cathode temperature substantially above normal, applying a high positive anode potential, holding the space current within a desired limit depending upon the radiating surface of the anode, and momentarily interrupting the space current by occasionally molmentarily interrupting the anode potentia 5. The method of activating electron emission tubes which includes increasing the cathode temperature substantially above normal, applying a high positive anode 'potental,

holding the space current within a desired limit depending upon the radiating surface of the anode,-momentari1y interrupting the space current by occasionally momentarily interrupting the anode'potential, and simultaneously cooling the envelope of the tube 6. The method of actlvatlng electron emission tub-es which includes increasing the oathode temperature substantially above normal,"

applying a high positive anode potential for about one to five minutes, holding the space current below a value which would cause vaporization of nickel in' the tube, and momentarily interrupting the space current by occasionally momentarily interrupting the anode potential.

7. Themethod of activating electron emission tubes'having a grid which includesincreasing the cathode temperature substantially above normal, applying a high positive potential to theanode, and a reduced potential to the grid in order to prevent overheat ing of the grid relative to the anode, and holding the space current Within a desired limit depending upon the radiating surface of the anode in order to prevent overheating of the-grid and anode.

8. The method of activating electron emission tubes having a grid which includes increasing the cathode temperature substantial ly above normal and applying a high positive potential to the anode and a reduced potential to the grid, and momentarily interrupting the space current by momentarily in- "terrupting the anode and grid potentials.

9. The method of activating electron emis sion tubes having a grid which includes increasing the cathode temperature substan-' tially above normal, applying a high positive potential to the anode and a reduced potential to the grid, holding the space current within a desired limit depending upon the radiating surface of the anode, and momentarily interrupting the space current by momentarily interrupting'the anode and grid potentials.

10. The method of activatmg electron emis sion tubes having a grid which includes increasing the cathode temperature substantially above normal, applying a high positive potential to the anode and a reduced potential to the grid, holding the space current within a'desired limit depending upon the radiating surface of the anode, momentarily interrupting the space current by momentarily interrupting the anode and grid'potentials, and simultaneously cooling the envelope of the tube. v

I 11. The method of activating electron emission tubes having a grid which includes increasing the cathode temperature substantially above normal, applying a high positive potential to the anode and a reduced potential to the grid in order to prevent overheating of the grid relative to the anode, holding the Ill space current below a value which would cause vaporization of nickel in the tube, and momentarily interrupting the space current by momentarily interrupting the anode and grid potentials.

12. An arrangement for reactivating electron emission tubes comprising a source of cathode heater current, means to vary the heater current, a source of direct anode potential, means to automatically limit the space current of the tube, and means including a resistance having a high positive temperature coefficient to automatically reduce the grid potential relative to the anode potentiial in order to prevent overheating of the gri 13. An arrangement for reactivating electron em ssion tubes comprising a source of cathode heater current, means to vary the heater current, a source of direct anode potential, means including a resistance having a high positive temperature coeflicient to limit the space current of the tube, and means to momentarily interrupt the anode potential.

14. An arrangement for reactivating elec-' tron emission tubes comprising a source of cathode heater current, means'to vary the heater current, a source of direct anode potential, means including a. resistance having a high" positive temperature coefiicient to limit the space current of the tube, means to momentarily interrupt the anode potential,

and means to cool the envelope of the tube.

15. An arrangement for reactivating electron emission tubes comprising a source of cathode heater current, means to vary the heater current, a source of direct anode potential, means to limit the space current of the tube, means to momentarily interrupt the anode potential, means connecting the grid to the source of anode otential, and means to reduce the grid otential relative to the anode potential in or er to prevent overheating of the grid.

16. An arrangement for reactivating electron emission tubes comprising a source of cathode heater current, means tova the heater current, a source of direct an e po- '50 rupt the anode potential, means including a resistance having a high positive temperature coeflicient connected between the grid and the anode of the tube in order to polarize the grid and to prevent overheating of the sagne, and means to cool the envelope of the tu e. r

18. An arrangement for reactivating electron emission tubes comprising a source of cathode heater current, means to vary the heater current, a source ofdirect anode potential, a plurality of resistances of different magnitude having high positive temperature coeflicients, means to apply the anode potential to the tube anode selectively through either of said resistances and to permit of momentarily interrupting of the anode potential, and means including a resistance having a high positive temperature coeflicient connected between the grid and the anode of the tube in order to polarize the grid and to prevent overheatin of-the same.

Signed at New Yor in the county of New York and State of New York this 25th day of October, A. D. 1929.

LESTER-L. JONES. JOSEPH A. FLANZER. EMIL REISMAN.

tential, a resistance having .a hi h positive temperature coeflicient connec in series with the anode, means to momentarily interrupt the anode potential, and means including a resistance having a high 'tive temperature coeflicient connected tween the grid and the anode of the tube in order to polarize the grid and to. prevent overheating of the same.

17. An arrangement for reactivating electron emission tubes comprising a source of cathode heater current, means toys-1y the an 6 heater .current, a source of direct in series- 

